Radio transmitting system



March 31, 1931. R. DAVIS ET AL RADIO TRANSMITTING SYSTEM Filed Jan.

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Charles \Nharn BY ATTORNEY Patented Mar. 31, 1931 UNITED STATES. ra'rnr orrice RDBERT L. DAVIS, OF PITTSBURGH, AND CHARLES W.

nonlfit, or WILKINSBURG, PENN- SYLVANIA, ASSIGNORS TO wns'rinerrousnnnnornie AND MANUFACTURING COM- PANY, A oonrona'rron or PENNSYLVANIA RADIO TRANSMITTING SYSTEM Our invention relates to radio transmitting systems, and it has particular relation to such systems in which a plurality of thermionic devices are connected in parallel in order to give a large power output.

One object of our invention is to provide means whereby the failure of one or more of a plurality of thermionic devices connected in parallel will not seriously interfere with the continuity of a program being transmitted.

'Another object of our invention is to provide means for automatically removing a defective tube from a circuit before a de-' structive arc has had anopportunity to form therein.

Another object of our invention is to provide means for automatically disconnecting a defective tube from a transmitting circuit, for stopping the transmission of the signal during the small interval of time required to disconnect the defective tube, and for automatically restarting the transmission after the defective tube has been disconnected.

In modern transmitting systems handling large amounts of power it is customary to connect groups of power-tubes in parallel in order that a suficient output may be ob tained. If, for any reason, one of the tubes of any one group starts drawing more than its proportionate share of plate current, by

reason of ionization, internal short-circuits,

or arcs, the functioning of the group is disturbed, and it is necessary that the defective tube be at once disconnected.

It is of course possible to discontinue the transmission while the defective tube is being removed by hand from the circuit, but this entails a very considerable break in the program, which is undesirable.

The apparently obvious solution of the problem, by using a fuse in series in the plate circuit of each tube, is impracticable In general, plate potentials of the order of 10,000 volts are now being used on power tubes, and in order to break the arc in a 10,000 volt direct current circuit it would benecessary to use a fuse well over three feet in length. Such fuse lengths are obviously out of the question, and T have accordingly provided an instantaneous-trip over-load relay tubes arran in the primary side of the transformer which is utilized to feed the rectifiers supplying plate potential, and have inserted the actuating coil of this relay inseries with the negative lead from the rectifier itself. In addition, v e have provided means whereby the entire transmitter is momentarily shut down during the'time it takes one of'the' fuses to open the circuit, and additional means for automatically restoring the transmitter to the operative state.v

The novel features which are considered characteristic of this invention areset forth with particularityin the appended claims. The inventionitself, however, both as to its organization and method of operation, together' with further objects and advantages thereof, will best be understood by reference to the following description taken in connec tion with the accompanying drawing.

The single figure of the drawing is a diagrammatic view of a group of modulator.

ged according to a preferred embodiment of my invention. Referring specifically to the drawing, a plurality of modulator tubes 1, each having a filament 2,'a grid 3 and a plate 4 are so arranged that filament potential therefor is supplied to the tubes through conductors 5 and Sin parallelfrom a source 7. The grids 3 are connected in parallel toa conductor 8, and interposed between the conductor and each of the grids is a radio frequency choke coil 11 and a fuse 12. The conductor 8 is connected to one end of the secondary winding 13 of an audio frequency transformer li, the other end of which is connected through a source 15 of grid biasing potential to the filament power supply conductor 5. The "primary winding 16 of the transformer la forms the output circuit of a speech amplifier (not shown).

The plates 4 of the tubes are connected in parallel to a conductor 17 which is also connected to the plates of the oscillator tubes (not shown). Interposed between the con ductor 17 and each of the plates is a fuse 18 of such a value that itwill open the circuit when the current therethrough reaches two or three times the normal current for the tube associated therewith. Plate potential for the tubes is supplied through a modulator choke coil 16 connected in the usual manner to a rectifier 22 which, in general, will comprise a plurality of individual rectifiers, arranged for single; or polyphase excitation. The negative terminal of the rectifier 1s connect ed through the actuating winding 24v of an instantaneous-trip over-load Switch 25 to the negative terminal of the filament poten} tial source 7 which terminal may also be connected to the filament terminals, of the oscillator tubes (not shown). In actual practice it may be necessary toadd a dash-pot, or

equivalent means, to the overload switch, in

element 32 and a conductor 35, which conductor is in turn connected to a movablearm 54, and to a fixed contact element 37 .associated with a starting button 38. A second contact element 41 isassociated with the starting button 38, from which element a conductor 42 leadsto the opposite side of the alternating potential source 26.

A manually operable switch 43 is connected across the starting button contact elements.

The-switching device 34 carries a plurality of movable arms on an insulating actuatingmember 44. An arm 45 is connected to one side of the alternating source 26 and has associated with it a contact elemen-t46 which is connected through a conductor 47 to the primarywinding 48 of a transformer 51 which energizes the rectifier 22. The other end of the primary winding 48 is connected to a conductor 52 which, in turn, connects to a contact element 53 withwhich is associated a movable arm 36 connected to the opposite side of the alternating potential source.

A contact element-55 is associated with the movable arm 54 previously referred to, and is connected bya conductor 56 to a contact element 57 associated with a stop button- 58. A. second contactelementi6l', associated with the stop button 58, is connected, by

7 means of'aconductor 62, to the conductor 52,

and, consequently, is connected to the contact element 53- associated=with the movable arnr 36 which is connected to the alternating po: tential source 26. i

It Will'be noted that-the movablemember short-circuiting which carries the three arms is biased to an open position by a spring 65. The stop button 58 is biased to a closed position by a spring 66, while the start button 38 is biased to an open position by a spring 67.

The circuit breaking or overload switch 25 is normally retained in a closed position under the 1nfluence of the force of gravlty. I The operation of a system arranged according'to our invention will now be explained.

the-other side of the source 26. The winding 33 of the starting switch 34' now being energized causes the movable arms 54, 36 and 45 to make contact with their respective-contact members 55, 53 and 46.

The startingbutton' is now released and a holding circuit for the starting switch may throughthe resistor 29, the overload switch Contact elements, the winding 33, the movable arm 54, the conductor 56, the stop'switch contact elements, the conductors 62 and 52, thecontact element 53, the movable arm 36', to the other side of the-power source 26. The power source 26 also applies potential to the primary winding 48 through movable members 36 and: 45' and conductors 52 and 47.

Power-for the rectifier associated with the oscillator tubes, if av separate rectifier is utilized, may also be applied through the conductors 52 and 47;.

If, fromvanycause, one of the modulator tubes becomes soft, permitting an excess ofplate current to flow therethrough, the

fuse 18 associated therewith immediately opens the circuit. As explained before, however, this'fuse is, of itself insuiiicientto interrupt the. high-potential direct current which is being supplied to the tubes. As soon, however, asthe current taken from the rectifier rises to a predetermined amount above normal, the overload switch 25 breaks the circuit through the holding winding 33, permitting the spring 65 to retract the element-44, thus movingall of the arms carried thereby away from theirrespective contacts.

This action is substantially instantaneous and, inasmuch asthe source 26 is not necessarily ofhigh potential, the circuit through the-primaryuof therectifierpower transformer is thus: broken. The b'reakingoftheprimary; circuitdeenergizes-therectifier 22 and be traced from one side of the source 26 stops the supply of plate potential to the modulator tubes.

The holding coil will not be again reenergized upon closing of the overload relay under the influence of gravity, inasmuch as the starting button 38 is biased to the open position.

By reason of the fact that the defective tube has been removed from the circuit by the action of the fuse associated therewith, the attendant may now restart the transmitter by again closing the starter button 38. In the interval, the defective tube may be replaced, or, if d sirable, continued transmission may be carried on with the remaining tubes.

The interruption, however, to the program occasioned by the necessity of personal attention and action on the part of the attendant is, in general, much longer than is desirable. VVe have, therefore, supplied the short-circuiting switch 43 which may be so actuated as to supply a semi-permanent connection across the starter button. The sequence of operations which take place when this switch is closed will now be explained.

Upon first depressing the starter button, as previously described, the primary of the rectifier will be supplied with energy, and the field of the holding coil 33 established. After the transmitter has thus been placed in operation, the attendant closes the short-circuiting switch. Upon failure of any of the tubes, the overload switch functions as previously described, breaking the holding current and causing the primary power supply to the rectifier to be interposed. Upon reclosing of the overload switch under the influence of gravity, a circuit may now be traced from one side of the source 26, through the contacts of the overload switch, through the holding coil 33, the conductor 35, the short circuiting switch. 43 and back to the other side of the source 26. It is thus obvious that the power supplied to the rectifier will only be interrupted for an interval of time corresponding to the opening and reclosing of the overload relay. This interval may, by proper adjustment of the relay, be so correlated to the length of time necessary for the fuse associated with the defective tube to open the circuit, that the tube is entirely disconnected from the highpotential conductor 17 before the reclosing of the overload relay.

It is accordingly apparent that, by our invention, we have provided a system whereby the failure of any one of a plurality of tubes connected in parallel will not cause a serious interruption in the continuity of transmitted signals. The restarting of the transmission may be either manually controlled or may be automatic, as described. Our invention, therefore, is of very great advantage when interruptions to a radio program are undesirable or where it is of prime importance that signals" of any other type" besubstantially continuous.

-Altho'ugh we have illustrated and dcthose skilled in the art and our invention is,

accordingly, not to be limited except as is necessitated by the prior art and by the spirit of the following claims.

IVe claim as our invention: v

1. In a transmitting system, a plurality of thermionic devices, means actuated by abnormal current conditionsin any of said-devices for temporarily discontinuing thesupply of power to all of said devices, and selfactuated means for subsequently restoring the power supply to only said devices.

2. In a transmitting system, a plurality of thermionic devices, a source of power therefor, means whereby the failure of any of said devices removes it from circuit and causes a temporary discontinuity in the power supplied to all of the devices, and self-actuated means for automatically restoring the power supply to only the remaining tubes.

3. In a transmitting system, a plurality of thermionic devices, a source of power therefor, means actuated by abnormal current conditions-in any of said devices for interrupting the supply of power thereto, and additional means for removing power supplypotentialfrom said devices during the interval of time required for said interrupting means to function.

4. In atransmitting system, a plurality of thermionic devices, a common source of power therefor, a plurality of like means severally associatedwith said devices and respec tively actuated by abnormal current conditions in the corresponding devices for interrupting the power supply thereto, and additional means, also actuated by abnormal current conditions, for de-energizing said power source.

5. In a transmitting system, a thermionic device, a source of plate potential therefor, means actuated by abnormal current con ditions in'said device for interrupting the supply of plate current thereto, and additional means also actuated by abnormal current conditions for de-energizing said plate potential source during the interval of time required to interrupt said plate current and for re-energizing said source automatically as soon as the defective thermionic device has been effectively removed from the circuit.

6. In a transmitting system, a thermionic device, means for deriving plate potential therefor from a primary power supply,

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means. omp i ing-a t ti g n dnd, a plurality of switching devices for control ling said primary power supply, and means whereby abnormal current demands upon 51 saidplate potential supply meanscause said actuating solenoid to permit said switching devices to interrupt the primary power supply to said plate potential supply means.

7. In a transmitting system, a thermionic device, a source of plate, potential for said device, a primary power supply for said source, means between the device and the source of; plate potential for permanently breaking the circuit therethrough upon the inception of abnormal current conditions, additional means responsive to abnormalcurrent conditions for interrupting the primary power supply,and means for at will rendering said primary power interrupting means 20 incapable of permanently interrupting said power supply.

8'. In comb nation, a plurality of thermionic devices, arectifier for supplying plate p0tentialthereto, a source of primary power 25- r"or'said rectifier, a fuse between the plate of each thermionic device and said rectifier, a connection including'the actuating winding of an over-load switch between said rectifier and; said devices, a switching device for in- 8 terrupting said primary power supply, said switching devicebeing under the control of said overload switch, whereby said primary power supply to said rectifier may be interrupted during the period of timerequired for we a fuse to respond to abnormal current conditions in the associated tube andremove said tubefrom conductive-connection to said rectifier.

9-. Ina transmitting; system, a plurality of .413. thermionic devices, a plate-potential-supply conductor common tosaid devices, meansactuated by: abnormal current conditions in. any of said. devices for temporarily depriving said conductor of potential, and self-actuated means for subsequently restoring plate potential to said conductor.

'10. In a transmitting system, a plurality of thermionic devices, a plate-potential-supply conductorcommon to said devices, means whereby the failure of any of said devices causes a temporary discontinuity in the vpotential applied to said conductor, means for removing the defective device from circuit, and self-actuatedmeans for automatically restoring plate-potential to said conductor.

In testimony whereof, we have hereunto subscribed our namesthis 31st day of December, 1926:

ROBERT LMDAVISL 69 CHARLES'W. HORN. 

